Warm weather sets up nitrogen concerns

The warmer than normal fall/winter and spring should raise concerns for growers about their soil nitrogen (N) situation.

The longer and warmer soils are, the more biological activity occurs in the soil. As a result, more of the N in the soil is converted to nitrate. This is true for all N in the soil, whether it's from commercial fertilizer, manure, or organic matter present in the soil.

With more nitrate in the soil to start the season and typical spring rainfall, we could see above average N loss by water moving through the soil and off the field through tile drainage before the crop can take it up.

Even if you wait until after planting to apply your N, there could still be above average N losses with normal Iowa spring rainfall.

The graph above, taken from the October, 2008 issue of the ISA On-Farm Network's On-Farm Update, shows the general trends in corn N uptake, soil temperature, and rainfall for Iowa.

To show how much this past winter differs from than the long term average, Peter Kyveryga, Ph.D., ISA On-Farm Network senior research associate, put the average precipitation and soil temperatures from the graph on the right into the graph on the left, along with soil temperature and precipitation data for the winter of 2011-2012.

Note that soil temperature in November 2011 was near the long-term average and the drop in temperature followed that average into December. However, soil temperatures in January and February were above the long-term average and with very little snow cover and above average air temperatures, by late March, the average soil temperature in Iowa was running more than 10 degrees higher than the long term average. What's more, the near-term forecast is for more above-average temperatures. This suggests at least a caution with regard to potential N losses.

Usually corn will take up only 60 percent to 70 percent of the total N it needs by tasseling time. So loss of N in June and early July can still have a major impact. A key factor to watch will be rainfall frequency and intensity over the next few weeks.

If you used a nitrogen stabilizer with your fall or spring application of N, or if you're considering it for applications yet to be made, it's important to realize that the effect of the stabilizers is measured in weeks, and we are talking about months of warmer conditions prior to tasseling.